1. Field of the Invention
The present invention relates to voltage protection circuits and, more specifically, to a voltage regulator with improved transient response capable of maintaining voltage within a predetermined range, which can be used as a voltage protection circuit.
2. Description of the Related Art
Excessive voltage can cause detrimental effects in electric appliances and electronic circuits. For example, lithium based batteries, including Lithium-Ion batteries and Lithium-Polymer batteries can be sensitive to and damaged by excessive voltage.
Excessive voltage can come from various external sources in different forms. Transient voltage spikes from external sources are one example. A transient voltage spike can be caused, for example, by an electrostatic discharge (ESD) event. Transient voltage spikes can cause damages in electronic circuits such as overcharging failure.
Currently, several approaches can be utilized to reduce or control impacts of external transient voltage events on various electronic circuits, in particular, semiconductor circuits. One approach widely used in the field of integrated circuit (IC) design is to clamp transient voltages on the inputs of the IC pins to protect the internal IC circuits from external voltage transient events. To do so, a shunt voltage regulator control circuit may be utilized for voltage protection. One example of a shunt voltage regulator is disclosed in U.S. patent application Ser. No. 09/545,135, entitled "Shunt Voltage Regulator with Self-Contained Thermal Crowbar Safety Protection," filed Apr. 7, 2000, which is hereby incorporated by reference for background purposes only. If a shunt voltage regulator is sufficiently fast and of sufficient bandwidth, the shunt voltage regulator can rapidly clamp all external voltage and current transients imposed therein from external sources. In this way, a circuit incorporating such a shunt voltage regulator can protect itself from external voltage transients.
FIG. 1 shows a simple prior art shunt voltage regulator circuit 100 (different from that disclosed in the aforementioned co-pending application). The circuit 100 includes a transistor 110 (such as a metal oxide semiconductor field effect transistor) having a first pole electrically coupled to the first node 102, a second pole electrically coupled to the second node 104 and a gate. The transistor 110 is capable of controlling an electrical current flowing from the first node 102 to the second node 104, i.e., ground, as a function of a voltage at its gate, which is also referred to herein as a controlling port. A voltage reference 150 generates a signal that has a predetermined potential difference from the second node 104. An amplifier 120, having a first input electrically coupled to the first node 102 and a second input electrically coupled to the signal from the voltage reference 150, generates an output electrically coupled to the gate of the transistor 110. The output of the amplifier 120 is thus a function of a voltage difference between the first node 102 and the second node 104.
The voltage regulator circuit 100 can be utilized in many applications. For example, the voltage regulator circuit 100 can be adapted to prevent overcharging of a battery 170 when the battery 170 is subjected to unusually high or excessive voltages, such as a voltage transient spike I. When an unusually high voltage is detected across the battery 170, the voltage regulator 100 increases the current bypassing the battery 170 through the first and second poles of the transistor 110, thereby reducing the voltage across the battery 170. Thus, by adjusting the current that bypasses the battery 170, the circuit 100 keeps the voltage across the nodes of the battery 170 within a desired range.
To achieve the desired protection, a shunt voltage regulator circuit should be optimized with respect to its circuit characteristics for fast response and wide bandwidth. One advantage for a voltage regulator circuit having fast response is that the voltage regulator circuit may protect itself, in addition to circuits the voltage regulator circuit may be adapted to protect, from excessive voltage transients. However, as is known in the art, such optimization may result in a shunt voltage regulator circuit that has poor steady state control accuracy. For example, in applications related to battery protection, this can result in an undesirable degradation of battery cell protection performance. On the other hand, a shunt voltage regulator circuit that is optimized for best steady state accuracy, as is required for good cell protection, is likely not to have the fast response and wide bandwidth required to adequately protect itself from excessive voltage transients.
There is therefore a need for a shunt voltage regulator that can have steady state control accuracy and the fast response and wide bandwidth with respect to external voltage transients.